Oxygen is an essential element for the lives of human beings and animals. In the regular processes of metabolism, the human body produces different kinds of Reactive Oxygen Species (ROS), and also possesses many ways to inactivate ROS. Under normal conditions, the rate of ROS production will not exceed that of consumption via metabolism by tissues. However, in certain circumstances (for example, due to radiation, environmental factors, and overload of ferric ions), ROS may increase to a level exceeding that under the regulation of normal metabolism, or when something went wrong (e.g., caused by genetic defects) in the protective biological mechanism, the excessive amount of ROS may cause damage to cells and tissues, and thus induces some diseases and even causes death. Proteins, lipids and DNAs are substrates to which ROS may attack. In a human body, there are about 1012 oxygen molecules entering into the cells every day, 1/100 of which destroy proteins, and 1/200 of which destroy DNAs. Especially when the human body's capacity of natural resistance is low, ROS may become very harmful due to such destructions on DNAs, proteins and lipids.
In a regular condition, the anti-radical defense system of the human body is effective against the harm to the body caused by the radicals. In a pathological condition, however, some of the damaging radicals may escape from elimination, and these escaped radicals and their products may act directly upon cellular DNA, proteins and lipids, causing some damages on DNA and inducing overoxidation of cell membrane lipids. These results caused by ROS are called oxidative stress, and the oxidative stress can influence regular gene expression, cell differentiation and necrocytosis. Today, oxidative stress is considered a factor causing many diseases.
Formation of cerebral atherosclerosis and thromboembolus may induce cerebral stroke. In the developed countries, the cerebrovascular diseases have been shown as the third leading cause for human death following heart diseases and tumors, and 5% of the elderly people over 65 years old suffer from cerebral stroke. In the United States, for example, more than 500,000 people are reported suffering from severe stroke, where 70-85% of the cerebral stroke is related to ischemic stroke, which has a mortality rate of 15-33%. The methods currently used for treatment of acute ischemic stroke include cytoprotection and thrombolysis, while cytoprotection is used to prevent cell death during ischemic reperfusion, and thrombolysis is used mainly to keep blood vessels clear using thrombolytic drugs during an early period of the disease. Despite much of the efforts, the cerebral stroke is still one of the most devastating diseases for medical treatments. One of the reasons that the current treatments for cerebral stroke are far from satisfactory is that so far no drugs have clearly demonstrated both thrombolytic and cytoprotective effects.
Parkinson's disease (PD) is a disease with clinical manifestations of resting tremor, myotonia, hypokinesia, and abnormal gait posture. It is currently known that the primary pathologic change of PD is of substantia nigra-striatum, which decreases the production of dopamine, and causes the above-mentioned clinical manifestations. The causes of substantia nigra degeneration are still unclear. Currently, most of the related studies suggested that oxidative stress plays an important role in the pathologic progress of PD.
Researchers found that many chemical substances show some radical-eliminating effects. Nitrones are a type of the compounds having a strong antioxidative activity and in vivo biological activity. The final products formed from the reactions of nitrones and radicals include hydroxylamine derivatives, aldehydes, amines, and nitroxide radicals.
Phenyl-tert-Butyl Nitrones (PBN) can react with radicals to form nitroxide radicals, while nitroxide radicals are able to directly react with and thus eliminate other radicals, and also are able to oxidize reductive metals so as to inhibit the Fenton reduction and the metal-catalyzed Haber-Weiss reaction. When aging accelerated mice were intraperitoneally injected with PBN daily, an increase of 33% in the lifespan of the mice was indicated (Edamatsu et al., Biochem. Biophys. Res. Commun. 211:847, 1995). When 24-month-old rats were intraperitoneally injected with 32 mg/kg of PBN daily for 9.5 months, it is indicated that lipid peroxidation reactions are diminished in two areas (cerebral cortex and globus pallidus) which are important for the cognitive function of the rats' brains, and at the same time, the cognitive ability for older rats is enhanced. More importantly, when the experiment was run for 32 months, 7 of the 11 rats injected with PBN were still alive (Sack et al., Neurosci. Lett. 205:181, 1996). Unfortunately, however, PBN is still merely applied in research and has not yet been developed into any drugs.
Tetramethylpyrazine (TMP, Chuxiongqin) is an active ingredient extracted from ligusticum wallichii (Chuanxiong), a traditional Chinese medicine. TMP has effects of radical elimination and thrombolysis/anticoagulation. TMP have been used clinically to treat cardiovascular and cerebrovascular diseases. It is founded that, however, the antioxidative effect of TMP is rather weak and its bioavailability is low. Clinically, multiple doses are needed for TMP to reach to an effective concentration.
Currently, there is no any effective curing method for the treatment of stroke, and the limited kinds of commercially available drugs are far from satisfactory due to inferior curative effects or toxic side effects. To be effective for any drugs to treat ischemic stroke, the following two functions are critical: thrombolysis and/or neuronal protection.